sergio masci wrote:
> On Sun, 2 Aug 2009, Dave Tweed wrote:
> > My point was, that if you add a simple boolean flag to the FIFO
> > structure, you CAN completely fill it, and this actually has negligible
> > impact on the overall code size, and does NOT affect its thread-safe
> > properties.
> 
> Ok, so please show how you would do this.

Oh, no, that would be telling! :-)

I've already written this up as part of the EQ quiz for Circuit Cellar #230
(September 2009), so you'll be able to read my solution there by the end of
the month. In the meantime, give it some thought. It's actually quite
straightforward.

> As a mater of interest what limitted expression-handling capabilities do 
> you see this code trying to get around (with the use of the temporary 
> variable).

Well, you wrote it with only one operation per line. With the "proc"
keyword, it wasn't immediately obvious that this was C code. I was also
suspicious of storing the length, head and tail of the FIFO in the array
with the data. You wouldn't ordinarily do that unless a language limitation
was forcing you to. I just assumed it was some personal language of yours
that was even lower-level than C, and I guessed that it was either easily
translatable to assembly, or that it had come from assembly to begin with.

In C, of course, you would simply write something like:

   tail = (tail + 1) % FIFO_SIZE;

Or, if your compilier isn't smart enough to optimize the % operator:

   tail = (tail + 1 == FIFO_SIZE) ? 0 : tail + 1;

Either of these is perfectly thread-safe; no standards-compliant compiler
would turn either statement into multiple assignments to tail.

-- Dave Tweed
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